The present invention relates to a method for providing a surface with carboxyl groups, to a surface which is provided in this manner with carboxyl groups, and to a product provided with such a surface which is suitable for exposure to blood.
Using conventional chemical processes, often it is not possible to selectively link ionogenic groups to a hydrophobic plastic or polymeric substrate surface. Terlingen, J. G. A. et al, (Journal of Colloid and Interface Science, 155, 55-65 (1993) which is incorporated by reference hereinto), describe a method for immobilizing sulphate groups on polypropylene. A similar method for immobilizing carboxyl groups on the plastic or polymeric surface appears however not to work (Terlingen, J. G. A. et al, Journal of Applied Polymer Science, 50, 1529-1539 (1993) which is incorporated by reference hereinto).
The present invention is based on the insight that when a plasma treatment is performed on a surface on which compounds with carboxyl groups are adsorbed, these carboxyl groups are not sufficiently resistant to the etching effect of the plasma treatment. It has been found from further research, however, that by making use not of compounds with carboxyl groups but of compounds with functional groups which can be converted after the plasma treatment into carboxyl groups which have a better resistance to the etching effect of the plasma treatment, the surface in question can thus be successfully provided with carboxyl groups via plasma treatment. After immobilization with the plasma treatment, the functional group then can be converted into a carboxyl group while avoiding loss or disappearance of the covalent bond between the compound and the surface.
In summary, the present invention therefore relates to a method for providing a surface with carboxyl groups, comprising the steps of successively:
(i) applying to the surface to be treated a compound with at least one functional group which can be converted into a carboxyl group; PA0 (ii) treating the surface onto which the compound has been applied with a plasma to immobilize the compound; and PA0 (iii) converting the functional groups of the immobilized compound into a carboxyl group.
Any type of functional group can in principle be applied. It is of course important that the functional group have a better resistance to the etching action of the plasma treatment than does a carboxyl group. Also, the compound having the functional group is to be capable of being immobilized by the plasma treatment by means of a covalent bonding to the surface, and the functional group should be substantially fully convertible into a carboxyl group. Functional groups meeting these requirements include carboxylate groups, aldehyde groups and alcohol groups.
Compounds with such a functional group can be applied to a plastic or polymeric surface in accordance with any known method, for instance a mechanical method comprising spinning a liquid onto the surface or applying a film to the surface, in both cases followed by evaporation of the solvent. Another method for applying the compound provided with a functional group to a plastic or polymeric surface includes adsorbing the compound from a liquid phase.
In those instances where the surface is a hydrophobic surface, it is further recommended that the compound containing the functional group have surfactant properties. An advantageous embodiment of the surfactant is a fatty acid salt such as alkali and alkali metal salts of fatty acids, or their corresponding alcohols and aldehydes. An example is the sodium salt of undecylenic acid, or sodium undecylenate.
For particular applications of the surface (for instance where the surface is intended for uses having exposure to blood), it can be advantageous that the surface is not only provided with carboxyl groups but also with SO.sub.3.sup.- groups under these conditions it is further recommended that a compound containing at least one SO.sub.3.sup.- group is applied to the surface being treated. According to a particularly advantageous embodiment, the compounds with the functional groups and the compounds with the SO.sub.3.sup.- groups can be adsorbed simultaneously.
Examples of compounds containing SO.sub.3.sup.- groups which can be used in this regard include organic sulphate (--C--O--SO.sub.3.sup.-) groups, sulphamate (--CNH--SO.sub.3.sup.-) groups and sulphonate (--C--SO.sub.3.sup.-) groups. Suitable organic compounds with sulphate and/or sulphonate groups are generally known. Compounds with sulphamate groups can be prepared according to the Warner method as generally disclosed in Warner, D. T. et al, J. Org. Chem. 23, 1133-1135 (1958), incorporated by reference hereinto. These compounds containing SO.sub.3.sup.- groups are preferably provided in the form of a surfactant, such as an analog of the corresponding fatty acid.
In order to avoid compounds being adsorbed on the surface but not immobilized by means of the plasma treatment, it is further recommended that the plastic or polymeric surface is subjected, after the plasma treatment, to a washing treatment. Compounds which are adsorbed but not immobilized are thus removed from the surface.
Another aspect of the present invention relates to a surface provided with carboxyl groups, which surface can be obtained by making use of the above described method according to the invention which comprises successively applying compounds containing the functional groups followed by a plasma treatment. This surface further also can be provided with SO.sub.3.sup.- groups.
In another aspect of the present invention, same relates to a product provided with such a surface which is suitable for exposure to blood. It has in any case been found that a surface provided with both sulphate functional groups and carboxyl functional groups can result in an improvement of the compatibility of such products with blood, making them especially suitable for in vivo applications.